Alloy steel for internal combustion valves or valve elements



Patented Jan. 3, 1939 v UNITED STATES PATENT OFFICE ALLOY STEEL FOR INTERNAL COMBUSTION VALVES R VALVE ELEMENTS Barry L. Frevert and Francis B. Foley, Philadelphia, Pa., assignors to The Midyale Company, Philadelphia, Pa.,- a corporation of Delaware No Drawing. Application October 15, 1938, Serial No. 235,238

12 Claims.

velopment has been made 'obsolete by the next advance in combustion engineering.

Many patents have been granted for alloy steel compositions suitable for the valve requirements of their corresponding dates; but today automotive engineers are demanding a steel having a combination of qualities not heretofore characterizing valve steel, or, so far as we know, steel adapted and intended for other uses. Such qualities may be enumerated as follows: Resistance to objectionable hot oxidation (scaling); freedom from pick-up; high hot strength, that is, strength, at operating temperatures, to withstand the stresses of service, especially the tendency of valves to umbrella or flatten (distort) with loss of sealing power; ductility, which the valve must have in some degree even when cold;

capacity of being readily forgeable and machin able; and ready hardenability.

No especial difllculty is involved in selecting known steel-alloying elements each having the effect of imparting to steel, in high degree, one or more of the qualities specified above as necessary. Thus chromium gives good scale resistance and assists in securing an adherent scale, and if used in limited proportion, increases cold ductility. Silicon increases scale resistance and also, if not used in too large percentage, ductility.

. out affecting materiallythe hardness when cold,

facilitates machining of the material.

Since the effectiveness of these alloying elements to impart the desired qualities .0 steel is known to us, and since we have also ascertained about which proportion of each alloying constituent gives the known result in the highest degree, it would seem to be a simple matter to associate with steel each of these constituents in the demonstrably ideal proportion and thereby produce an ideal valve steel. But experiment has shown such a steel is of inferior quality and lacks, in greater or less degree, all the characteristics which theoretically it ought to possess. In fact the knowledge of the properties possessed by the alloying constituents is merely a starting point for working out a composition having the desired qualities.

The reason for this apparently contradictory" state of facts is that no single approximately maximum quality can be imparted to the steel by any one of the specified alloys that does not have the effect of impairing or even destroying some quality that would otherwise be imparted impossible to secure the desired hot strength,

notwithstanding the presence in the steel of alloys that otherwise would insure both high hot strength and cold ductility.

Manganese, especially when associated with chromium, is ideal to secure, especially when used in high proportion, extraordinary highhot strength; but when used in considerable proportion it decreases scale resistance, and when used in excess of 2.75% it decreases forgeability and may virtually destroy such cold ductility as might'otherwise be imparted to it by other constituents. Further, it is well known that, when used in considerable proportion, it produces the phenomena of large grain size and coarse crystallization, giving a bad effect so far as concerns working properties both hot and cold.

While silicon is known to give good scale resistance and, in moderate proportions, to aid in securing cold ductility, it reduces hot strength and if used in fairly large proportion it has a pronounced weakening effect at elevated tem-- peratures.

Nickel is promotive of good cold ductility and forgeability and increases hot strength, but it is bad for scale resistance if used in too high proportion.

From the foregoing it will be understood that the problem presented is to devise a composition containing all or most of the foregoing ingredients, each in such proportion as to secure the parted to the steel by the other ingredients. In other words, the amount of each element must be so adjusted as to secure its beneficial eflect to as high degree as is consistent with avoidance of a serious degree of its detrimental effect. This involves holding the percentages of all the constituent elements within rather close limits. Such a composition, which is the subjectmatter of this invention, excludes most possible chrome-nickel-manganese-silicon-copper compositions and definitely excludes all of the few known chrome-nickel-manganese-silicon-copper compositions. r

We have found that the proportions of each of the ingredients must be within the following proportion ranges: The steel must .be a low or medium carbon steel, the carbon percentage, permissibly as low as .05% or even lower, but not exceeding 1.0% and preferably not exceeding .65%. Chromium preferably from 14 to 15.5%, and not over 17% or under 11%. Manganese over .65% and under 2.75% and preferably .9 to 1.2%. Silicon 2 to preferably 3 to 4%. Nickel may vary within a wide range, but should be over 2% and under 8%, and is preferably between 5 and 7.5%. Copper may vary from 1 to 5%, and is preferably from 2.25 to 3%.

Specific examples of alloy steel possessing in high degree all the qualities hereinbefore enu- The lower limitation on the percentage of chromium is imposed by the fact that any smaller percentage requires, in order to secure high scaling resistance, the use of a higher proportion of silicon, which seriously reduces strength at elevated temperature; while the higher limitation on the percentage of chromium is imposed by the fact that a higher percentage neutralizes the high hot strength effect produced by manganese and nickel, and the cold ductility effected by the addition of nickel. With silicon under 2.5% the scaling resistance is too low even with a maximum percentage of chromium, while if in excess of 5% it impairs hot strength and forgeability even with maximum additions of nickel and manganese.

It is possible, however, to reduce the silicon to below 2.5% if aluminum be substituted in part therefor. Aluminum, unlike silicon, in small amounts may, associated with a reduced percentage of silicon, appreciably increase hot strength and give an adherent scale, but if in excess, or if associated with too high a percentage of silicon, it seriously lowers hot strength and it renders the steel much less ductile when cold and in some compositions it wholly destroys cold ductility. Copper should be present in an amount over 1.0% and usually over 2%, since it increases hot strength, permits a slight but appreciable reduction in manganese or nickel, or both manganese and nickel, and, without materially reducing hardness, greatly facilitates machining. It is highly desirable that the steel shall be sub-austenitic in character or at least that it should not readily revert to a dominantly ing novel per se in alloysteel containing material percentages of chromium and smaller percentages position as our invention independently of the novelty of the composition per se, since no such valves or valve elements have ever been made or sold, nor has the special utility of such a composition for that use ever been recognized or disclosed.

While the addition of small quantities of other known steel-alloy constituents is not prohibited, it will be understood that no such alloy can be added which may neutralize the beneficial effect of any of the alloys set forth in the claims.

What we claim and desire to protect by Letters Patent is:

1. An alloy steel which contains carbon .05 to 1.0%, chromium 11-17%, manganese .65 to 2.75%, silicon 2 to 5%, nickel 2 to 8%, copper 1 to 5%, the balance of the composition being substantially iron, said steel being characterized by exceptional strength at high temperature, high resistance to scaling, ductility when cold as well as when hot, and ready machinability and hardenabillty.

2. An alloy steel which contains carbon .05 to .65%, chromium 14 to 15.5%, manganese .90 to 1.3%, silicon 3 to 4%, nickel 4.5 to 7.5% and copper 2.25 to 3%, the balance of the composition being substantially iron, said steel being characterized by exceptional strength at high temperature, high resistance to scaling, ductility when cold as well as when hot, and ready machinability and hardenability.

3. An alloy steel which contains carbon .05 to .65%, chromium'not varying more than two per cent from 14.75%, nickel not varying more than two per cent from 6%, silicon not varying over one per cent from 3.5%, manganese not varying over .5% from 1.1%, copper not varying over one per cent from 2.5%, the balance of the composition being substantially iron, said steel being characterized by exceptional strength at high temperature, high resistance to scaling, ductility when cold as well as when hot, and ready machinability and hardenability.

4. An alloy steel of the composition and having the characteristics defined in claim 1 in which the percentage of carbon does not exceed .65%.

5. An alloy steel of the composition and hav ing the characteristics defined in claim 1 in which the percentage of chromium is between 13.5 and 16%.

6. An alloy steel of the composition and having the characteristics defined in claim 1 in which the percentage of manganese is between .9 and 1.5%.

7. An alloy steel of the composition and having the characteristics defined in claim 1 in which the percentage of silicon is between 3 and 4%.

8. An alloy steel of the composition and having the characteristics defined in claim 1 in which the percentage of nickel is between 4 and 7.5%.

9. An alloy steel of the composition and having the characteristics defined in claim 1 in which the percentage of copper is'between 2 and 3.5%.

10. A valve or valve element for internal combustion engines having the composition and characteristics set forth in claim 1.

11. A valve or valve element for internal combustion engines having the composition and characteristics set forth in claim 2.

HARRY L. FREVERT. FRANCIS B. FOLEY. 

